The standard gauges, &c., in use in the United States have been obtained from Sir Joseph Whitworth, or duplicated from those made by him with the aid of measuring and comparing machines. It has been found, however, that different sets of these gauges did not measure alike, the variations being thus given by Mr. Stetson, superintendent of the Morse Twist Drill and Machine Co.
At the time the Government established the use of the standard system of screw threads in the navy yards, ten sets of gauges were ordered from a manufacturer. His firm procured a duplicate set of these and took them to the navy yard in Boston and found that they were practically interchangeable. He also took them to the Brooklyn Yard Navy. The following tabular statement shows the difference between them:—
| Size. | Navy Yard Male Gauge. | Morse Twist Drill and Machine Co. Male Gauge. | Morse Twist Drill and Machine Co. Female Gauge. | |||||||||||
| 1⁄4 | 0 | .25 | 0 | .25 | Interchanged | |||||||||
| 5⁄16 | .313 | .313 | „ | |||||||||||
| 3⁄8 | .375 | .3759 | ||||||||||||
| 7⁄16 | .437 | .437 | Interchanged | |||||||||||
| 1⁄2 | .505 | .505 | „ | |||||||||||
| 9⁄16 | .562 | .564 (-) | „ | |||||||||||
| 5⁄8 | Damaged | .626 | „ | |||||||||||
| 3⁄4 | .7505 | .751 | „ | |||||||||||
| 7⁄8 | .876 | .8758 | „ | |||||||||||
| 1 | 1 | .00075 | 1 | .00075 | „ | |||||||||
| 1 | 1⁄8 | 1 | .125 (+) | 1 | .125 (-) |
| ||||||||
| 1 | 1⁄4 | 1 | .25 | 1 | .25 | Interchanged | ||||||||
| 1 | 3⁄8 | 1 | .375 | 1 | .375 | „ | ||||||||
| 1 | 1⁄2 | 1 | .5 | 1 | .5 (-) | (-) | ||||||||
| 1 | 5⁄8 | 1 | .6245 | 1 | .624 | (-) | ||||||||
| 1 | 3⁄4 | 1 | .749 | 1 | .749 | Interchanged | ||||||||
| 1 | 7⁄8 | 1 | .8745 | 1 | .874 | (-) | ||||||||
| 2 | 1 | .999 | 1 | .999 | ||||||||||
| The sign (-) means that the piece is small, but not enough to measure. | ||||||||||||||
| The sign (+) means that the piece is large, but not enough to measure. | ||||||||||||||
The advantages to be derived from having universally accepted standard subdivisions of the yard into inches and parts of an inch are as follows:—
When a number of pieces of work of the same shape and size are to be made to fit together, then, if their exact size is not known and there is no gauge or test piece to fit them to, each piece must be fitted by trial and correction to its place, with the probability that no two pieces will be of exactly the same size. As a result, each piece in a machine would have to be fitted to its place on that particular machine, hence each machine is made individually.
Furthermore, if another lot of machines are afterwards to be made, the work involved in fitting the parts together in the first lot of machines affords no guide or aid in fitting up the second lot. But suppose the measurements of all the parts of the first lot are known to within the one ten-thousandth part of an inch, which is sufficiently accurate for practical purposes, then the parts may be made to measurement, each part being made in quantities and kept together throughout the whole process of manufacture, so that when all the parts are finished they may go to the assembling or erecting room, and one piece of each part may be taken indiscriminately from each lot, and put together to make a complete machine. By this means the manufacture of the machine may be greatly simplified and cheapened, and the fit of any part may be known from its size, while at the same time a new part may be made at any time without reference to the machine or the part to which it is to fit.
Again, work made to standard size in one shop will fit to that made to standard size in another, providing the standard gauges agree.
The Pratt and Whitney Company, of Hartford, Connecticut, in union with Professor Rogers, of Cambridge University, in Massachusetts, determined to inspect the Imperial British yard, to obtain a copy of it, and to make a machine that would subdivide this copy into feet and inches, as well as transfer the line measurements employed in the subdivisions into end measures for use in the workshops, the degree of accuracy being greater than is necessary in making the most refined mechanism, made under the interchangeable or standard gauge system. The machine made under these auspices is the Rogers-Bond Universal Comparator; Mr. Bond having been engaged in conjunction with Professor Rogers in its construction.
The machine consists of two cylindrical guides, upon which are mounted two heads, carrying microscopes which may be reversed in the heads, so as to be used at the front of the machine for line measurements and on the back for end measurements.
